Vulcanizable and vulcanized products from polyethylene and process for their production



United States Patent VULCANIZABLE AND "ULCANIZED PRODUCTS FROMPOLYETHYLENE AND PROCESS FDR THEIR PRODUCTION Peter J. Canterino andAlbert N. De Vault, Bartlesville,

Okla., assignors to Phillips Petroleum Company, a corporation ofDelaware No Drawing. Application July 12, 1954 Serial No. 442,892

13 Claims. (Cl. 26094.9)

This invention relates to the halogenation and dehalogenation ofhydrocarbon polymers. In one aspect it relates to a process forproducing a vulcanizable polymeric material. In another aspect itrelates to a novel vulcanized composition.

It is known in the art to produce solid polymers of ethylene and otherolefins by polymerization of ethylene or other olefins at very highpressure in the presence of an oxygen-containing catalyst. It is alsoknown in the art to halogenate and to dehalogenate such solid polymers,the halogenation and the dehalogenation being conducted as separatesteps. Recently, it has been found that solid polymers of ethylene andother olefins can be produced at relatively low pressures bypolymerizing ethylene or other olefins in the presence of a catalystcomprising chromium oxide, usually associated with another oxide. Thisprocess and the products thereof are described in the copendingapplication of I. P. Hogan and R. L. Banks, Serial No. 333,576, filedJanuary 27, 1953, now abandoned.

This invention provides a novel and improved process for halogenatingand dehalogenating a polymer of an olefin to obtain a partiallydehalogenated material which can be vulcanized to produce a novelcomposition. The vulcanized composition has many uses, some of which arespecifically described herein.

According to this invention, there is provided a process whereby apolymer of an aliphatic olefin, e. g. ethylene, can be halogenated andat least partially dehalogenated in substantially a single step and in asingle reaction zone to produce a vulcanizable product. The process isconducted by reacting the polymer, at a temperature above its meltingpoint, with a halogenating agent under such conditions that halogenationand partial dehalogenation occur substantially simultaneously. Thisresult is effected by conducting the reaction between the polymer andthe halogenating agent at, a temperature in the range l50-300 C.,preferably 175275 C. When the reaction is begun at a temperature in thelower part of the broad range of temperature, e. g. ISO-175 C., it ispreferred to raise the temperature to a value in the range l75-300 C.after substantial halogenation has occurred. It is often preferred toconduct the reaction in the range l75-30() C., in which rangehalogenation and at least partial dehalogenation occur without furtheradjustment of the temperature. The halogenation-dehalogenation reactioncan be conducted in the presence of a dehydrohalogenation catalyst suchas metallic magnesium, metallic zinc, magnesium chloride, zinc chlorideor barium chloride. However, the reaction proceeds satisfactorily in theabsence of a catalyst and it is, therefore, often preferred to conductthe reaction without a catalyst. The reaction can be conducted in thepresence of a halogenation catalyst of the type known in the art or thereactants can be irradiated as, for example, with sunlight orultraviolet light. It is ordinarily preferred to use irradiation becausethis manner of operation introduces no foreign materials into thereaction mixture.

2,850,490 Patented Sept. 2, 1958 Alternatively, the reaction can beconducted in the absence of a halogenation catalyst. Althoughdehydrohalogenation appears to constitute a substantial part of thedehalogenation, the invention is not limited to such a reactionmechanism.

As the halogenating agent, an elemental halogen of the group chlorine,bromine, or iodine or a compound which yields these elements under thereaction conditions can be used. Examples of such halogen-yieldingcompounds or halogenating agents are carbon tetrachloride, carbontetrabromide, carbon tetraiodide, hexachloroethane, chloroform,iodoform, bromoform, and phosgene.

The preferred polymer used as the starting material can be any normallysolid or tacky polymer of an aliphatic olefin and ordinarily will be anormally solid polymer of a monoolefin such as ethylene, such polymersbeing produceable as previously described herein. The term normallysolid polymer of ethylene, as used herein, contemplates bothhomopolymers and copolymers of ethylene, such as copolymers of ethylenewith propylene. Although a preferred polymer is a normally solid polymerof ethylene, viscous or semisolid polymers of olefins as disclosed inthe cited application of Hogan and Banks can be used. Normally solidpolymers of propylene, l-butene, l-pentene, or l-hexene can also beused. A preferred type of polymer is one produced by polymerizing analiphatic l-olefin having a maximum chain length of 8 carbon atoms andno chain branching nearer the double bond than the 4-position in thepresence of a chromium oxide polymerization catalyst as more fullydisclosed in the cited application of Hogan and Banks.

Further, according to this invention, the product of the halogenationand partial dehalogenation can be vulcanized to produce novel materialswhich have a wide variety of uses. Thus, the vulcanized materials can bemolded to form shaped articles, extruded to form pipes or tubes,extruded onto wire to form insulation therefor, or applied to varioussurfaces as coating materials or heat insulators. Also, in accordancewith the invention, a pigment can be added to the recipe, prior tovulcanization, and in such a case a composition is obtained which, aftervulcanization, is useful as a marking composition, useful, for example,in crayons, pencils and similar instruments. Suitable pigments which canbe incorporated into the composition are carbon black, graphite,titanium dioxide, malachite and iron oxide. Other pigments known in theart can also be used to obtain the color desired. The amount of pigmentadded is generally within the range of 5 to parts by weight per parts byweight of the halogenated and partially dehalogenated polymer althoughlarger or smaller quantities can be employed. A preferred range is 25 to60 parts of pigment, and a more preferred range is from 40 to 60 parts.It will be understood by those skilled in the art that the optimumproportion of pigment will depend upon, among other things, the natureof the specific pigment used.

The term vulcanization as used herein is intended in the same generalsense as that term is used in the rubber or elastomer art. Thus, thevulcanization ordinarily comprises heating the halogenated and partiallydehalogenated polymer, for example at a temperature in the range 350*400F., with a vulcanizing agent such as elemental sulfur, zinc oxide,magnesium oxide, or other known vulcanizing agent such as a suitableorganic sulfur compound. Sulfur is the vulcanizing agent which is mostwidely used.

Vulcanized products ranging from flexible, leathery substances to hardplastics are obtained from solid polyethylene, according to thisinvention, by first treating the polymer with a halogen such aschlorine, bromine, or

iodine or a halogenated hydrocarbon such as carbon tetrachloride orhexachloroethane at an elevated temperature to obtain an unsaturatedpolymeric material which is then mixed with a vulcanizing agent, andsuch other compounding ingredients as desired, and vulcanized.

When treated in accordance with one manner of practicing this invention,a solid ethylene polymer is first melted, the temperature is adjusted tothe desired level, e. g. 175-300" C., and the halogen or halogenatedhydrocarbon is introduced while the reaction mixture is stirred tofacilitate contact of the halogen with the polymer. While the scope ofthe invention is not dependent upon any particular reaction mechanism,it is believed that halogenation of the polyethylene first occurs,followed by dehydrohalogenation. The halogenating agent can beintroduced throughout the entire reaction period or the addition ofhalogenating agent can be stopped and heating continued to effectfurther dehydrohalogenation. The type of product can be controlled bythe amount of halogen introduced, the length of the heating period, ifany, which follows, and the temperature. The reaction time will usuallyrange from 1 to 30 hours but can be longer or shorter. The unsaturatedpolymer thus obtained is then mixed with a vulcanizing agent and suchother compounding ingredients as desired such as activators,accelerators, fillers, etc., and the compounded stock is thenvulcanized.

The production of the unsaturated polymers is elfected essentially inone step, the only agent added being a halogen or a halogenatedhydrocarbon, such as carbon tetrachloride or hexachloroethane. It is notnecessary that a halogenation step be effected first in the presence ofa solvent or dispersing medium followed by a separatedehydrohalogenation step in which a dehydrohalogenating agent isemployed. By merely controlling the reaction conditions, a vulcanizablematerial is readily obtained in a single step.

Instead of operating at a high temperature throughout the reactionperiod, i. e., l75-300 C., it is sometimes preferred to use a lowertemperature during the addition of the halogen or halogenated compound(carbon tetrachloride or hexachloroethane) and then to raise thetemperature toward the end of the reaction period. For example, thehalogen can be introduced into the melted polyethylene at a temperaturebelow 175 C. and the temperature then raised and maintained at thehigher level for the desired period.

The halogen or halogenated compound can be added over a period of from 1to hours and the mixture then heated, if desired, for a period up to 20hours or longer. During the heating period, it is frequently preferredto flush the reactor with an inert gas such as carbon dioxide ornitrogen to purge the system of hydrogen halide which has been formedduring the reaction. During the entire reaction period, i. e., duringthe addition of halogen and also during the heating period, the reactionmixture is stirred or otherwise agitated.

When chlorine, carbon tetrachloride, or hexachloroethane is employed,the amount preferred is generally in the range from 8 to 60 parts byweight per 100 parts polyethylene although larger quantities can beadded if desired. With other halogens, corresponding amounts, based onthe equivalent weights, are used. While the products frequently containhalogen, it is generally considered desirable, if the halogen ischlorine, that the halogen content not exceed 10 percent by weight andpreferably that it be less than 7 percent by weight. A suitable range ofchemically bound chlorine content is from 2 to 7 weight percent.Corresponding amounts of the other halogens can be present instead ofchlorine.

This invention provides a method for obtaining polymeric materialsranging in unsaturation from 2 to percent or higher (2 to 15 doublebonds per 100 ethylene units in the polymer) from polyethylene. It isbelieved 0 rate was 11 gallons/hour.

'4 that these unsaturated materials are free from cross linkages, i. e.,the halogenation and dehydrohalogenation occur in the same polymzrchain. These materials, when compounded and vulcanized, yield valuableproducts which range from flexible leathery substances to hard plastics,depending on the details of the method of preparation. The vulcanizedproducts are much more solvent resistant than the polyethylene fromwhich they were prepared and are also resistant to the action of acidsand alkalies. The unvulcanized products have little strength and cannotbe molded satisfactorily, while the vulcanized materials can be employedin the manufacture of various molded articles and can be extruded intopipe or onto wire as insulation. They can also be used as coatingmaterials.

Example I Ethylene was polymerized, over a chromium oxidesilica-aluminacatalyst containing 2.4 weight percent chromium as chromium oxideoperating at 320 F. and a pressure of 400 p. s. i. g., a space velocity(volumes liquid/volume reactor/hour) of 6, and a feed containing 3weight percent ethylene is isooctane. The ethylene feed rate was 1.3pounds/hour and the isooctane flow The polyethylene obtained wasinsoluble in benzene and acetone. It had a molecular weight of 13,640.

One hundred fifty grams of the polyethylene described above was chargedto a reactor provided with a stirrer and a Dry-Ice condenser. Thepolyethylene was melted, the temperature was adjusted to 160 C., and 66grams of chlorine was introduced over a period of approximately fourhours while the reaction mixture was stirred and irradiated withultraviolet light. The temperature was maintained at l50170 C. Afterintroduction of the chlorine, stirring was continued and the mixture washeated to 250 C., over an 8-hour period to complete thedehydrochlorination. The reactor was flushed with carbon dioxide duringthe heating period to purge the system of HCl which was formed duringthe reaction. The product had a chlorine content of 5.05 weight percentand an unsaturation of 6.9 percent (an average of 6.9 double bonds perethylene units). Unsaturation was determined by the iodine monochloridetitration method.

The unsaturated product was compounded in accordance with the followingrecipes:

The mixtures were milled on a hot mill and vulcanized by heating at 300F. for 45 minutes. The samples were tested on an Instron tester using0.2 inch cross-head speed. The following results were obtained:

Sample Tensile, Elonga- N 0. p. s. 1. tion, Description of Productpercent I 1,090 92 Flexible, leathery product, insoluble in toluene. H1, 065 4. 5 Hard, somewhat brittle product, in-

soluble in toluene.

For control purposes an uncompounded sample of the unsaturated productwas heated under the same conditions used for vulcanization of thecompounded samples. A hard, crumbly material, soluble in toluene, wasobtained. It could not be removed from the mold without breaking.

The vulcanized material containing carbon black (recipe II) marks onpaper in much the same manner as an ordinary pencil. The marks do notsmear and are easily erasable. Thus, it is evident that the vulcanizedproduct of this invention can be used as a binder for graphite in themanufacture of pencils. Other types of carbon black, such as channelblack. lamp black. acetylene black, high-abrasion furnace black, and thelike. can be used as pigments. This type of product can be fabricatedinto leads for mechanical pencils.

Example II A sample of polyethylene (400 grams) prepared as described inExample I, and having a molecular weight of 10,050 was charged to areactor provided with a stirrer and a Dry-Ice condenser. Thepolyethylene was melted, the temperature was adjusted to 160 C., and 120grams of chlorine was introduced over a period of approximately sixhours. During the addition of the chlorine the temperature ranged from150-170' C. The mixture was stirred throughout this period, andirradiated with ultraviolet light. Stirring was continued while thetemperature was raised to 240250 C. and the reactor was flushed withcarbon dioxide as in Example I. The product has an unsaturation of 11.6percent, as determined by the iodine monochloride titration method, andcontained 3.88 weight percent chlorine.

A portion of the product was compounded in accordance with the followingrecipe:

Parts by weight Polymer 100 Stearic acid 2 Sulfur 2 Agerite alba(hydroquinone monobenzyl ether) 1 N,N-dimethyl-S-tert-butylsulfenyldithiocarbarnate 1.5 Zinc oxide 5 The sample was cured minutes at 307F.. and physical properties were determined. Physical properties werealso determined on a sample of chlorine-treated but uncompoundedpolyethylene and on the original polyethylene. The following resultswere obtained:

Compoundw firi' inal ar'd Vull'n-z" mpounded Polycuni7cd Farnpleethylene Sample Percent un"aturntion. 11.6 116 0. Percent cl l rine 3.83 3.8 0. Compoundcd and \"ul Ye No No. Tensile, p. s. i... 1.105 1.272.060. Elongation. pcrccpt 45 15 10. Softening print, F. 1 2."0 2532250. Flex temper: ture, F 38 ?0. Brittle. Electrit al properties:

Di sipaiien factor 0 0032 0.0031 (Hl005. Dielectric constt-nt. 2.94 2.042. 35. 1 me.

Dis ipation f='ctor. 0.0170 0 0100 1 0.0005 Dielectric const:'nt .752.50 2.32. Vol. percent such in tohrcne:

T .1 37.2 I l -integrated Partially soluble. At 212 I"., 21 Ill 124Dissolved...

l Rnlihery product; does not lose its shape at 200 F.

2 Kiloeycle.

3 Megan-wit.

The foregoing data show that a rubbery material having desirableelectrical insulation properties and low solubility in toluene isprepared according to this invention.

Example III A sample of commercial polyethylene 1 (400 grams) having amolecular weight of 11,500 was melted, the temperature was adjusted to160 C. and 96 grams of chlorine 1 Prcslimul 1y prep :it-il liypolymerization in the presence of an organic peroxidotypc catalyst at :1pressure of the order of 500010,000 p. s. i.

was introduced over a 6-hour period while the mixture was stirred andirradiated with ultraviolet light. The procedure was similar to thatdescribed in the preceding examples. During chlorination, the reactionmixture became very viscous. After addition of the chlorine, the mixturewas heated to 240250 C. and stirred while the reactor was flushed withcarbon dioxide. The product had an unsaturation of 6.05 percent asdetermined by the iodine monochloride titration method, and contained5.6 weight percent chlorine.

A portion of the product was compounded using the recipe given inExample II. The sample was cured 45 minutes at 307 F., and physicalproperties were determined. Physical properties were also determined onthe treated but uncompounded product and on the original polyethylene.The following results were obtained:

l I 'Co nponnd d; Ori inal and Vul- Uncompounded Polynniz d Sampleethylene Sample Percent unsaturation 0, 05 Percent. chlorine 6Cornpounded and vulcanized Yes Tensile, p. s. i fill-7 Elongation,pcrcent.. 0 t Softening point, F hl Flex temperature, F -72 Electricalproperties:

Dissipation faetoru" 0 0020 0.00.34 (0.0005. Dielectric constant 3. 052.80. 2.3. 1 1110.

Dissipation factor... 0. 0203 0.0189 0.0005. Dielectri (")nstant 2 7'1)2.3. Vol. percent swell in tolu ne 115. 5 Soluble.

at: 78 F.

1 As in Example II.

The foregoing data show that useful products are obtained, according tothis invention, from polyethylene other than those produced bypolymerizing ethylene in the presence of a chromium oxide catalyst.

Example IV Polyethylene was prepared in a manner similar to thatdescribed in Example I to give a product having a molecular Weigh of9,000. To grams of this material heated to 200 C., 30 grams of chlorinewas introduced over a two-hour period while the mixture was stirred.

Example V Ten milliliters (16 grams) of carbon tetrachloride was addedto grams of the polyethylene described in Example IV and the mixture washeated to C. At the end of this period, more carbon tetrachloride wasintroduced over a period of six hours until a total of 17 ml. (27 grams)had been added. Toward the end of the reaction the temperature increasedto 210 C. The mixture was stirred throughout the reaction period. Theproduct contained 2.8 weight percent chlorine and had an unsaturation of5.2 percent as determined by the iodine monochloride titration method.This product can be vulcanized as previously described.

Example VI unsaturation of 3.6 percent as determined by the iodinemonochloride titration method. Infrared analysis on a sample which hadbeen purified by crystallization from methylcyclohexane showed theproduct to be unsaturated. This product can be vulcanized as previouslydescribed.

The vulcanizable products of this invention generally contain from about1 to about weight percent, and frequently from 2 to 7 weight percent,chemically combined halogen, and have an unsaturation in the range 2 topercent (average number of double bonds per monomer unit) and frequently3 to 12 percent. However it is within the scope of the invention toetfect substantially complete halogen removal especially wherebromination and/or iodination agents are used.

The molecular weights mentioned herein are determined by the methods ofKemp and Peters, Ind. Eng; Chem. 35, 1108 (1943), and Dienes and Klemm,J. App. Phys. 17, 458-471 (June 1946).

The molecular weights were calculated according to the equation 4.03X10XNiX14 1.303

wherein M is the molecular weight and N, is the intrinsic viscosity asdetermined for a solution of 0.2 gm. of polymer in 50 cc. of tetralin at130 C.

While certain examples, process steps and compositions have beendisclosed for purposes of illustration, the in vention is clearly notlimited thereto. The essence of the invention is that there is provideda process for the substantially simultaneous halogenation and partialdehalogenation of a polymer of an aliphatic olefin and that the processproduces a vulcanizable composition, which, when vulcanized, yields auseful and novel vulcanizate. It will be evident to those skilled in theart that variation and modification within the scope of the disclosureand the claims can be practiced.

The foregoing examples and discussion relate primarily to batch-typeoperation. It should be understood that the same reactions can becarried out in a continuous manner, using suitable equipment, as will beevident, to those skilled in the art, from this disclosure.

We claim:

1. A process which comprises reacting a normally solid polymer of analiphatic olefin with a halogenating agent at a temperature in the rangeof 150 C. to 300 C. for a period of l to 30 hours, elfectinghalogenation and at least partial dehalogenation with removal ofhydrogen halide in substantially a single step, the dehalogenation beingeffected at a temperature of at least 175 C. and within said range,regulating reaction conditions of temperature and time to provide aproduct having an unsaturation of from 2 to 15 percent and a combinedhalogen content notexceeding 10 percent by weight and recovering theresulting halogenated product.

2. The process of claim 1 in which the halogenation and dehalogenationare carried out in the temperature range of 175 C. to 300 C.

3. The process of claim 1 in which the normally solid polymer is apolymer of ethylene and the halogenating agent is selected from thegroup consisting of chlorine, bromine, iodine, and materials capable ofyielding these halogens.

4. The process of claim 3 in which the halogenating agent is elementalchlorine.

5. The process of claim 3 in which the halogenating agent is added overa period in the range of 1 to 10 hours and heating is continued for anadditional period up to 20 hours after introduction of the halognatingagent has ceased.

6. The process according to claim 5 wherein said halogenating agent iselemental chlorine.

7. The process according to claim 5 wherein said halogenating agent iselemental bromine.

8. The process according to claim 5 wherein said halogenating agent iselemental iodine.

9. The process according to claim 5 wherein said halogenating agent iscarbon tetrachoride.

10. The process according to claim 5 wherein said halogenating agent ishexachloroethane.

11. A writing instrument comprising, as the marking element thereof, avulcanizate of halogenated polymer prepared according to the process ofclaim 1 containing from 5 to parts by weight of a pigment selected fromthe group consisting of carbon black, graphite, titanium dioxide,malachite, and iron oxide.

12. A vulcanizable product prepared according to the process of claim 1.

13. A product of the vulcanization of a halogenated material prepared inaccordance with the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 528,Wiley and Sons, New York (1952).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,850,490 September 2, 1958 Peter J. Canterino et al.

It is herebfl certified that error appears in the -printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 2, line 64, for "350-400 read 250-400 column 4, line 23,

for ethylene is" read ethylene in column '7, line 23, in the equationfor "1.303" read 2.303 column 8, line 17, for "halognating" readhalogenating Signed and sealed this 21st day of April 1959.

SEAL) ttest:

KARL H. AXLINE ROBERT C. WATSON Anesting Officer Commissioner of Patents

1. A PROCESS WHICH COMPRISES REACTING A NORMALLY SOLID POLYMER OF ANALIPHATIC OLEFIN WITH A HALOGENATING AGENT AT A TEMPERATURE UN THE RANGEOF 150*C. TO 300* C. F OR A PERIOD OF 1 TO 3 HOURS, EFFECTINGHALOGENATION AND AT LEAST PARTIAL DEHALOGENATIIN WITH REMOVAL OFHYDROGEN HALIDE IN SUBSTANTIALLY A SINGLE STEP, THE DEHALOGENATION BEINGEF FECTED AT A TEMPERATURE OF AT LEAST 175* C. AND WITHIN SAID RANGE,REGULATING REACTION CONDITIONS OF TEMPERATURE AND TIME TO PROVIDE APRODUCT HAVING AN UNSATURATION OF FROM 2 TO 15 PERCENT AND A COMBINEDHALOGEN CONTENT NOT EXCEEDING 10 PERCENT BY WEIGHT AND RECOVERING THERESULTING HALOGENATED PRODUCT.